This invention relates to an improved collagen sausage casing and to a process to manufacture the casing. The ideal collagen sausage casing must be of sufficient strength to be processed, to stuff or fill the casing with a meat emulsion to make the sausage and yet be tender when eaten. These characteristics are opposites, and efforts to increase the processing strength or machinability of the casing invariably result in diminishing the tenderness or eating quality of the casing. Conversely, attempts to improve the tenderness or eating quality of the casing have resulted in casings which have insufficient strength to withstand the stresses encountered during the stuffing, linking or other handling and machining of the casing.
Enzymes have been employed to treat natural animal intestine casings in an attempt to obtain a balance of the desired properties. The natural casings were immersed in an enzyme solution either before or after stuffing with the meat emulsion. These processes, disclosed in U.S. Pat. Nos. 2,314,313 and 2,321,621, treat only the exterior surfaces of the casings, and the interior portion of the casing is usually not effectively treated.
Proteolytic enzymes have also been used in prior art processes to treat the source of collagen employed in making the gels which are extruded to form collagen casings. These processes treated the animal hides or collagen dispersions with various enzymes to alter the characteristics of the collagen dispersion prior to extrusion. The enzymes were usually denatured or destroyed by various treatments prior to the extrusion of the collagen to form the casing, or after the casing was formed but prior to drying and finishing. Examples of such processes are disclosed in U.S. Pat. Nos. 2,920,000; 3,034,852; 3,071,477; 3,314,861; 3,373,046 and 3,681,093. For example, in U.S. Pat. No. 3,373,046, hides which had been treated with lime are treated with enzymes to assist in the removal of calcium from the limed hides. The enzyme is destroyed or denatured before the acid is added to form an extrudable, acid-swollen mass. In U.S. Pat. No. 3,314,861 insoluble collagen of steer hide is treated with various enzymes to completely solubilize the collagen into a solution from which a casing may be prepared. In U.S. Pat. No. 3,681,093, collagen is treated with an enzyme and acid to partially solubilize the collagen, i.e., to the extent of 10-20 percent. A casing is formed by extruding a fluid mass of acid swollen, partially solubilized collagen.
In these prior art processes; the enzymes are employed to either break down the non-collagen protein in the hide or to break down the collagen itself. In order to perform this function, the enzyme is incubated with the pieces of hide or other sources of collagen for periods of time ranging from 5 to 48 hours. The enzyme is added to the source of collagen prior to the usual acid swelling step.
Enzymes have also been used to treat collagen which is used to form films. The films did not have the wet tensile strengths that are required of a collagen casing material. Examples of such processes are disclosed in U.S. Pat. Nos. 3,529,530 and 3,664,844.